It's implied that Charlie Calello and Joe Long didn't join the group until after Bob left, but they'd been working with the group for a while before that.
The famous handshake between Frankie and Bob didn't happen after a concert, but in Bob's dad's house.
Mary Delgado's last name was not Delgado. (I think she requested they not use her real name.)
Get the JB book...there are a few more elaborations there.
"This thread reads like a series of White House memos." — Mister Matt
I'm sure there are plenty more-- to make the story more dramatic, time is compressed, Lorraine is a compilation rather than a representation of one actual person, etc. You'd have to pick up some bios of the guys and the group if you really wanted the nitty gritty differences.
'"Contrairiwise," continued Tweedledee, "if it was so, it might be; and if it were so, it would be; but as it isn't, it ain't. That's logic."'
~Lewis Carroll
Thanks LizzieCurry, I'll check it out to find out more information.
The book is really interesting, although light on quotes from Tommy...
A few other ones I can think of that may or may not be in the book (I can't remember and don't have the book on me right now):
Marianne (as mentioned in the song) was Frankie's second wife and she's not mentioned in the show, but at that point it's kind of late to introduce a new character.
There's at least one song that Bob, Frankie, Nick, and Tommy perform in the show that I believe was actually written after Nick and/or Tommy had left the group. I can't remember which song, though.
Bob Gaudio was from the Bronx, and although they don't mention this in the show, they never really say he's not from Jersey, either.
"This thread reads like a series of White House memos." — Mister Matt